The present invention relates to a device and a method for operating an internal combustion engine.
The invention also relates to a computer program and a computer program product associated with the device and method for operating an internal combustion engine.
DE 41 41 051, EP 1 573 194, EP 1 333 157, and DE 10 2006 057 247 have already disclosed a device and method for operating an internal combustion engine in which a heat engine is coupled to the internal combustion engine. In them, at least one heat exchanger is integrated at least into an exhaust line of the internal combustion engine. The heat exchanger is integrated into a working cycle of the heat engine as an evaporator or superheater. The heat engine functions in accordance with the Rankine cycle.
In the Rankine cycle, a pump first feeds a fluid through the heat exchanger, which is situated for example in the exhaust line of the internal combustion engine, causing the fluid to be evaporated and superheated. A vapor produced in this way is then conveyed into a decompression apparatus in which the vapor drives an expansion machine. Then the remaining vapor is condensed in a subsequent condenser. Finally, the fluid travels through the same Rankine cycle again. The turbo element is coupled, for example, directly to the internal combustion engine, thus increasing the output of the internal combustion engine. Alternatively or in addition, the expansion machine drives one or more auxiliary units, in particular a generator, thus improving the exploitation of the fuel.
The above-mentioned devices and methods are based on the fact that the combustion of a fuel/air mixture in the internal combustion engine produces a hot exhaust that supplies a sufficient quantity of heat to operate the heat engine. If the internal combustion engine is being operated in an operating state such as overrunning or braking mode, in which no hot exhaust is being produced by the combustion, then the quantity of heat that is absorbed by the heat exchanger is insufficient to keep the Rankine cycle going. In addition, if a long absence of a sufficient heat quantity occurs, then the cooling of the heat-absorbing heat exchanger also increases the amount of time that is required to restart the Rankine cycle.